1. Technical Field
This invention relates to signal gain control. In particular, this invention relates to controlling input signal level without compromising the strength of desired content in an output signal derived from the input signal.
2. Related Art
Signal processing systems ranging from remote sensing systems to wireless communication systems enhance dynamic performance using automatic gain control. Automatic gain control adjusts input signal gain as a function of another parameter, such as received signal level. If a signal level is too high or too low, the automatic gain control may attenuate or amplify the input signal to keep the received signal level within a specified range.
Automatic gain control operates in isolation, however. Downstream processing operates on the gain-controlled signal, but without knowledge of what gains were applied or why they were applied. The downstream processing produces an output signal based on or derived from the input signal. Thus, the strength, quality, or content of the output signal may be detrimentally influenced by the automatic gain control.
In speech processing systems, automatic gain control may suppress desired speech signal content in the input signal. Subsequent processing stages which depend on sufficient levels of speech signal are hampered by the suppression. Voice recognition is particularly sensitive to speech signal level, and may yield inaccurate results ultimately stemming from isolated application of automatic gain control. Wireless voice networks also are sensitive to input signal levels which must lie within established ranges for proper transmission.
There is a need for a system that overcomes the detrimental impact of automatic gain control on an output signal.